Disposable electronic-cigarette cartridges have recently been proposed containing a hygroscopic (e.g. cotton-wool) wad impregnated with a viscous liquid substance containing nicotine and possibly also aromas. In actual use, the electronic cigarette heats the disposable cartridge to slowly volatilize (vapourize) the viscous liquid substance impregnating the hygroscopic wad.
Disposable cartridges of this sort are manufactured by producing a disposable cartridge with an open top end; inserting a dry hygroscopic wad inside the disposable cartridge; filling the disposable cartridge with a calibrated amount of liquid substance; and then plugging the open top end of the disposable cartridge with a plug permeable to vapour (i.e. that keeps in the liquid substance, but lets out the vapours produced by heating the liquid substance).
The most critical stage in the manufacture of disposable cartridges is filling them with the liquid substance. This is an extremely time-consuming job, partly on account of the liquid substance fed into the disposable cartridge having to impregnate the hygroscopic wad (a relatively slow process), and partly on account of the viscous nature of the liquid substance itself (i.e. its high density, which slows down its movement). As a result, currently used disposable cartridge manufacturing methods are extremely slow (i.e. have a low output rate) on account of the time taken to fill the disposable cartridges with the liquid substance.
To speed up the filling process, it has been proposed to pressure-feed the liquid substance into the disposable cartridges, so as to ‘force-fill’ the cartridges. Pressure-feeding the liquid substance into the disposable cartridges, however, has several drawbacks. Firstly, the pressure of the liquid substance may deform the hygroscopic wad and/or the disposable cartridge itself; which deformation may be destructive and at the very least is almost always permanent, i.e. with no springback recovery once the cartridge is filled and the pressure removed. Secondly, when pressure-feeding the liquid substance into the disposable cartridges, it is almost impossible to prevent some of the liquid substance from leaking from the cartridge and so fouling both the cartridge and the filling unit.